In the title compound, [Ru(C10H10N6)(C7H10N2)3](PF6)2·C4H10O, the RuII cation is coordinated by one tris(1-pyrazolyl)methane (Tpm) and three dimethylaminopyridine (dmap) ligands in a slightly distorted octahedral geometry. The asymmetric unit consists of one complex cation, two hexafluoridophosphate anions and one diethyl ether solvent molecule in general positions. Although quite a large number of ruthenium complexes of the facially coordinating tridentate Tpm ligand have been structurally characterized, this is only the second one containing three pyridyl co-ligands. The average Ru-N(Tpm) distance is 2.059 (12) Å, while the average Ru-N(dmap) [dmap = 4-(dimethylamino)pyridine] distance is somewhat longer at 2.108 (13) Å. The orientation of the dmap ligands varies greatly, with dihedral angles between the pyridyl and opposite pyrazolyl rings of 14.3 (2), 23.2 (2) and 61.2 (2)°.

The new compound (I) was synthesized simply by substituting all three chloride
ligands in RuIIICl3(Tpm) (Llobet et al., 1988) with
4-(dimethylamino)pyridine (dmap) under reducing conditions, by adapting a
method used previously to prepare [RuII(Tpm)(vpy)3][PF6]2 (vpy =
4-vinylpyridine) (Calvert et al., 1983). The isolated yield is
reasonably high, while the blue colour is attributable to traces of the
Ru(III) form of the complex which is rendered relatively electron-rich by the
three dmap ligands. If a drop of ascorbic acid solution is added to an acetone
solution of (I), the solution turns pale yellow immediately, indicating
complete reduction to the Ru(II) species. The signals in the 1H NMR spectrum
show no broadening, consistent with an adequately pure sample.

The complex salt (I) shows an intense, broad UV absorption band at λmax =
322 nm in acetonitrile. This absorption is attributable to d→π*
metal-to-ligand charge-transfer (MLCT) transitions
from the Ru-based HOMO to the LUMOs localized on the dmap ligands. An
additional band at λmax = 264 nm is ascribed to ligand-based
π→π* transitions, while a very weak band at λmaxca 590 nm is due to the blue-coloured Ru(III) form that disappears upon reduction
with ascorbic acid. By way of comparison, the compound
[RuII(Tpm)(py)3][PF6]2 shows a MLCT band at 344 nm in acetonitrile;
this is red-shifted when compared with that for (I) because the py ligands are
more strongly electron-accepting than dmap.

Cyclic voltammetric studies on (I) reveal a reversible RuIII/II wave at
E1/2 = 0.75 V versus. Ag–AgCl, much lower than the
value of 1.25 V
for [RuII(Tpm)(py)3][PF6]2 recorded under the same conditions
(acetonitrile, 0.1 M [N(n-Bu4)]PF6, 100 mv s-1,
ferrocene/ferrocenium standard at 0.44 V). This difference reflects the strong
electron-donating ability of the dimethylamino substituents.

The molecular structure of the complex cation in (I) is as indicated by 1NMR
spectroscopy, with a facially coordinating Tpm ligand and a slightly distorted
octahedral coordination geometry. The N(Tpm)–Ru–N(Tpm) angles cover the
range ca 85.3–86.5°, and the other angles at the Ru centre show small
deviations from the ideal values. The average Ru–N(Tpm) distance of 2.059 (5) Å is similar to that reported for [RuII(Tpm)(py)3][PF6]2 (2.074 (16) Å; Laurent et al., 1999). The average Ru–N(dmap) distance of
2.108 (5) Å is the same as that reported for
[RuII(tpy)(phen)(dmap)][PF6]2 (tpy = 2,2';6',2''-terpyridine; phen =
1,10-phenanthroline) (2.107 (2) Å; Bonnet et al., 2003), but a
little
shorter than that found in [RuII(dmap)6]Cl2·6EtOH (2.131 (1) Å;
Rossi et al., 2008). A significantly shorter average Ru–N(dmap)
distance has been reported for the trinuclear complex in
trans-[(dmap)4RuII{(µ-NC)OsIII(CN)5}2][PPh4]4.10H2O
(2.089 (13) Å; Rossi et al., 2010). Considerably longer
Ru–N(dmap)
distances have been reported also, for example 2.333 (4) Å when positioned
trans to a tellurocarbonyl ligand in
trans,cis-RuIICl2(dmap)2(CTe)(H2IMes) (H2IMes =
1,3-dimesitylimidazolin-2-ylidene) (Mutoh et al., 2010), and as
long as
2.338 (3) Å when located trans to a carbene ligand in
trans,cis-RuIICl2(dmap)2(PCy3){CH(C6H4)-4-NMe2}
(Dunbar et al., 2011).

The orientation of the dmap rings in (I) with respect to their opposite
pyrazolyl rings is highly variable, with the following dihedral angles: 61.2°
between N1/C1/C2/C3/C4/C5 and N9/N10/C26/C27/C28; 23.2° between
N3/C8/C9/C10/C11/C12 and N11/N12/C29/C30/C31; 14.3° between
N5/C15/C16/C17/C18/C19 and N7/N8/C23/C24/C25. A similar orientational
variability of the py rings is found in [RuII(Tpm)(py)3][PF6]2, with
corresponding dihedral angles of 70.0, 20.6 and 10.2° (Laurent et al.,
1999).

The structure was solved by direct methods. The H atoms were placed in
calculated positions (methyl H atoms were allowed to rotate but not to tip)
and were refined isotropically with Uiso(H) = 1.2 Ueq(C)
(1.5 for methyl H atoms) using a riding model with C—H lengths of 0.95(CH),
0.99(CH2) & 0.98(CH3) Å.

Geometry. All e.s.d.'s are estimated using the full covariance matrix. The cell e.s.d.'s
are taken into account individually in the estimation of e.s.d.'s in
distances, angles and torsion angles; correlations between e.s.d.'s in cell
parameters are only used when they are defined by crystal symmetry

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor
wR and goodness of fit S are based on F2, conventional
R-factors R are based on F, with F set to zero for
negative F2. The threshold expression of F2 >
σ(F2) is used only for calculating R-factors(gt) etc.
and is not relevant to the choice of reflections for refinement.
R-factors based on F2 are statistically about twice as large
as those based on F, and R- factors based on ALL data will be
even larger.